This project was also made with an EEG, specifically one that had eye-tracking as well. The painting would slowly start filling in wherever they were looking.
As their brain produced more alpha waves associated with relaxed or meditative attitudes, the canvas would be painted more quickly. As each image plays, music associated with the color of each pixel also plays. All of it is designed to further help relax the viewer.
Finally, if the eye-tracking detects that the image is no longer interesting a new image is selected to slowly start painting instead.
Though before you start fiddling around with this, it might be worth checking your knowledge on the brain first: